1. Brief Description of the Invention
The present invention relates to methods and apparatus for testing and analyzing operability of fuel gas control systems for appliances such as water heaters, furnaces, cooking ranges and ovens, decorative fireplace inserts, pool heaters and similar gas fired appliances. More particularly, the present invention relates to methods and apparatus for testing operability of a thermocouple device of a fuel gas control system and for testing operability of a safety valve solenoid-high temperature electricity cut off fuse, (ECO fuse) circuit of a fuel gas control system under simulated load conditions.
2. Background of the Invention
Gas control systems for appliances are commercially available and widely used. A gas control system supplies fuel gas to an appliance under conditions such that the fuel gas may be safely ignited in the appliance firing chamber. In situations where safe ignition of the fuel gas cannot be ensured, the gas control system will prevent fuel gas from entering the appliance firing chamber. Such gas control systems are available for both natural gas and liquefied petroleum gas, (LPG), fuels.
Such gas control systems are well known and understood and only such description will be given here as is required to describe the method and apparatus of the present invention. An illustrated description of a typical gas control system may be found in xe2x80x9cService Manual For Residential Gas Water Heater Controlxe2x80x9d, published in 1997 by White Rogers division of Emerson Electric Company.
A gas control system for an appliance comprises several elements acting cooperatively to achieve the functions of safely controlling flow of fuel gas to the appliance firing chamber and ensuring ignition of the fuel gas. Typically, a gas control system comprises a fuel gas control valve having a safety valve solenoid, an ECO fuse, a pilot flame device, an appliance burner and a heat sensing thermocouple device. The safety valve solenoid, ECO fuse and thermocouple device are connected in a series electrical circuit. In one type of gas control system, a pilot flame from the pilot flame device is maintained continuously for activating the thermocouple device and for igniting the fuel gas at the appliance burner. In another type of gas control system, fuel gas is ignited at the appliance burner by a spark gap igniter and the gas burner flame activates the thermocouple device. The ECO fuse senses temperature in the medium heated, (water, or air), in an appliance and the ECO fuse breaks upon sensing high temperature in the heated medium, for stopping flow of fuel gas to the appliance burner and the pilot flame device.
A gas control valve in a typical fuel gas control system comprises a solenoid activated safety valve and a manual shunt valve. The solenoid activated safety valve is opened, for flow of fuel gas through the gas control valve, upon the solenoid being activated by a millivolt DC current generated by the thermocouple device upon sensing a pilot flame at the pilot flame device in the appliance firing chamber. The manual shunt has three positions: xe2x80x9coffxe2x80x9d, which prevents flow of fuel gas through the gas control valve; xe2x80x9cpilotxe2x80x9d, which allows flow of fuel gas to the pilot device when the solenoid safety valve is open; and xe2x80x9conxe2x80x9d, which allows flow of fuel gas to the pilot device and the appliance burner when the solenoid safety valve is open. The gas control valve also comprises a manual override which, upon manual activation, opens the safety valve when the manual shunt is in xe2x80x9cpilotxe2x80x9d position, for allowing ignition of a pilot flame at the pilot flame device before the thermocouple device senses temperature sufficiently high to generate a millivolt DC current sufficient to activate the solenoid and open the safety valve.
The thermocouple device comprises a bimetallic thermocouple, a first electrical conductor connected to one leg of the bimetallic thermocouple, and a second electrical conductor connected to the other leg of the bimetallic thermocouple. The first electrical conductor is commonly a copper tube which runs from the first leg, of the thermocouple to the body of the gas control valve. The second electrical conductor is an electrically insulated wire which runs from the second leg of the thermocouple, through the copper tube, for electrical connection to the safety valve solenoid. The copper tube of the first electrical conductor: connects the first leg of the thermocouple to the body of the gas control valve; supports the second electrical conductor from the second leg of the thermocouple to the gas control valve for connection to the safety valve solenoid; and provides support for the thermocouple in the appliance firing chamber. A thermocouple, as used in gas control systems, generally has a DC out put voltage in the range of about 7 to 30 millivolts, depending on the bimetallic elements and the temperature to which the thermocouple is exposed. The thermocouple and safety valve solenoid are matched to ensure that the thermocouple will generate sufficient DC voltage to operate the solenoid under normal operating conditions.
The thermocouple, ECO fuse and safety valve solenoid are in a closed loop, series electrical array such that a millivolt DC current flows from the thermocouple second leg, through the second electrical conductor, through the ECO fuse into the input of the safety valve solenoid. From the safety valve solenoid output, the millivolt DC current flows through the body of the gas control valve, through the first electrical conductor to the thermocouple first leg, thus completing the closed loop electrical circuit.
The ECO fuse is a thermal fuse located in the medium being heated by the appliance. For example, in the water tank or the air outlet plenum of a water heater or an air heater. In the event the medium becomes overheated, the ECO fuse will melt and break the electrical connection between the thermocouple and the safety valve solenoid, thus shutting off fuel gas to the main burner and the pilot burner of the appliance.
3. Description of Pertinent Art
It is well known that appliance gas control systems often fail in operation. Such failures may be caused by a variety of causes, such as failure of the safety valve solenoid, failure, or melting, of the ECO fuse, or failure of the thermocouple. Often, the causes of such failures are difficult to determine. The gas control valve and ECO fuse are supplied as a unit and the thermocouple device is supplied as a separate unit. Neither unit is subject to repair and must be replaced when the unit fails. As each unit is relatively expensive, it is desirable to determine which unit has failed and to replace only the failed unit.
A thermocouple device may be easily checked by disconnecting it from the gas control valve and connecting the first and second electrical conductor to a millivolt meter. A pilot flame is then applied to the thermocouple and the DC voltage generated is registered by the millivoltmeter. In such a test, if the millivolt output from the thermocouple device is at least about 7 millivolts, the thermocouple device is considered operational. This test is referred as an xe2x80x9cunloaded testxe2x80x9d of the thermocouple device. This test of the thermocouple does not test the safety valve solenoid and ECO fuse portion of the fuel gas control system.
A second test method, employing a special adaptor and a millivolt meter, for testing the entire electrical circuit of a fuel gas control system, (safety valve solenoid, ECO fuse, thermocouple device), under loaded conditions is disclosed in xe2x80x9cService Manual For Residential Gas Water Heater Controlxe2x80x9d, published 1997, White Rogers division of Emmerson Electric Company. For this method, the thermocouple device is disconnected from the gas control valve and a special adaptor is connected between the gas control valve and the thermocouple device. The special adaptor reconnects the thermocouple device, safety valve solenoid and ECO fuse and also allows a millivolt meter to be connected to both leads from the thermocouple. According to this method, after the adaptor is installed and the millivolt meter is connected to each of the thermocouple leads, the gas control valve is set to xe2x80x9cpilotxe2x80x9d position and the manual override of the safety valve is engaged. The pilot flame is then ignited and is allowed to heat the thermocouple for about 3 minutes. The millivolt meter is observed during this heating period. A 7 millivolt output from the thermocouple device should be sufficient to energize the safety valve solenoid and hold the safety valve open such that flow of gas to the pilot device will continue when the safety valve manual override is released. According to this method, if the thermocouple device output measured by the millivolt meter does not rise to at least 7 millivolts at the end of the 3 minute test period, (after ensuring that the pilot flame is properly directed onto the thermocouple), then the thermocouple device is judged faulty and should be replaced. On the other hand, if the thermocouple output rises to at least 7 millivolts but the pilot flame will not remain lit when the safety valve manual override is released, the gas control valve is judged faulty and should be replaced.
The test method described in the paragraph above tests the thermocouple under load conditions and tests the gas control system electrical circuit as a whole, but does not test the safety valve solenoid and ECO fuse portion of the electrical circuit. That is, a condition may exist where the ECO fuse is intact and the safety valve solenoid is operational, but the thermocouple device does not generate a millivolt current sufficient to energize the safety valve solenoid. In such case, according to the above test method, the recommendation is to replace the gas control valve when, in fact, the thermocouple device should be replaced with one having a higher millivolt output.
Now, according to the present invention, I have invented apparatus and a methods for testing operability of a safety valve solenoid and an ECO fuse of a fuel gas control system under electrical load conditions to determine whether the safety valve solenoid and ECO fuse, are functionally operable and for separately testing the millivolt output of a thermocouple device in the fuel gas control system.
The advantages of the apparatus and test methods of the present invention include the ability to determine whether the safety valve solenoid and ECO fuse are operable separately from the thermocouple device and whether the safety valve solenoid and thermocouple device are compatible for operating together as elements of a fuel gas control system. These and other advantages of the methods and apparatus of the present invention will be described in the Detailed description of the invention which follows.